System and method for image-based alignment of an endoscope

ABSTRACT

Systems and methods for endoscopic procedures employ a first technique to ensure initial correct alignment of an endoscope ( 100 ) with a desired target ( 10 ). A reference image ( 51 ) is then acquired from an imaging arrangement associated with the endoscope. During a subsequent stage of the procedure, tracking of the endoscope position relative to the target is performed partially or entirely by image-based tracking by comparing features in real-time video image ( 52 ) produced by imaging arrangement with features in the reference image ( 51 ). The feature comparison may be performed visually by a user, or may be automated to offer more specific corrective suggestions to the user.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to endoscopy techniques and, inparticular, it concerns a system and method for image-based alignment ofan endoscope during at least part of an endoscopic procedure.

The present invention will be exemplified in the context of a system asdescribed in the co-assigned PCT application published as WO 03/086498entitled “Endoscope Structure and Techniques for Navigation in BranchedStructure” to Gilboa, which is hereby incorporated by reference in itsentirety. The aforementioned patent application discloses a method andapparatus in which a thin locatable guide, enveloped by a sheath, isused to navigate a bronchoscopic tool to a target location within thelung, aimed in particular to deliver treatments to the lung peripherybeyond the bronchoscope's own reach. The coordinates of the target arepredetermined based upon three-dimensional CT data. A location sensor isincorporated at the locatable guide's tip. The enveloped guide isinserted into the lung via the working channel of a bronchoscope. First,the bronchoscope's tip is directed to the furthest reachable location inthe direction of the target. Next, the guide is advanced beyond the tipof the bronchoscope towards the designated target, based on thecombination of the CT data and the position of the guide's tip asmeasured in body coordinates. When the guide's tip at the target, theguide is withdrawn, freeing the enveloping sheath for insertion abronchoscopic tool. In order to prevent the distal end portion of thesheath from sliding away from the target, the sheath is locked to thebronchoscope's body and the bronchoscope itself is held steadily toprevent it from slipping further into the lungs or outwards. Because theairways in the periphery of the lung are narrow, approximately in thesame dimensions as the sheath, sideways movements are extremely limited.

The above system may also be used to navigate the tip of thebronchoscope to a target located inside the main bronchus and not onlyto targets in the periphery of the lungs. Although for suchcentrally-located target the physician has direct visualization of thescene in front of the bronchoscope, it is not always sufficient forvisually identifying the designated targets, since many of these targetsare hidden in the tissue outside the airways. Hence, it is a benefit tocombine the CT data into the navigational aids also for targets insidethe main bronchus, where the bronchoscope can reach and direct visionexists, but yet the target itself is hidden.

When using the navigation system for navigating the tip of thebronchoscope itself, many of the mechanical features of the locatableguide described in WO 03/086498 are not needed. Specifically, thesteerability of the guide is not needed, and the enveloping sheath isalso not needed. However the principle of using a separate locatableguide having a location sensor at its tip and being inserted into theworking channel of a regular bronchoscope actually changes thebronchoscope from a non-locatable bronchoscope to a locatablebronchoscope, thereby offering major advantages as will become clear.

As in the prior art apparatus, the locatable guide can be inserted intoand withdrawn from the bronchoscope's working channel as needed. Unlikethe periphery of the lung, the central airways are much wider than thebronchoscope. As a consequence, when the tip of the bronchoscope is ontarget, it can move sideways in addition to sliding in and out.Therefore stabilizing the bronchoscope's tip during treatment is a threedimensional task, involving the operation of the steering ability of thebronchoscope. An example for the importance for maintaining the locationof the bronchoscope's tip at the designated target during the insertionof the bronchoscopic tool is the use of the Transbronchial HistologyNeedle, by which a needle is guided towards a target such as a lymphnode which neighbors the main bronchus from the outside and thus isinvisible to the bronchoscope image but its coordinates are known fromthe CT data. Any mistake in directing the needle may result not only infailure of the procedure, but worse, in causing damage to vital organssuch as the aorta or other major blood vessels.

In principle, the same methods as presented in WO 03/086498 may be usedin the context of the major airways. Specifically, by using the locationof the tip of the bronchoscope as measured by the location measurementsensor, a directing display is produced corresponding to a simulation orschematic diagram of the view from the distal tip of the guide, which isbased on the relative location of the target versus the position of thetip of the guide in six degrees of freedom. In the central airways, thisview is supplemented by the direct video image from the bronchoscopeimaging arrangement. Based on these two displays, the physician bringsthe tip of the bronchoscope to the target. When the tip of thebronchoscope is correctly aligned with and adjacent to the target (FIG.7), the guide with the location sensor is withdrawn (as shown in FIG.8), thereby freeing the bronchoscope's working channel for insertion abronchoscopic tool FIG. 9 a). Once the locatable guide is released, thedirecting display can no longer function for directing the tip totarget. Instead, the physician has to hold the bronchoscope as steadilyas possible during withdrawal of the guide and the insertion of thetool. If the bronchoscope slips from the target location (for example,as shown in FIG. 9 b), the physician may notice the chance of positionin the video image, but has no effective tool available to help himreturn the tip of the bronchoscope reliably to the desired target (otherthan reinserting the guide and repeating the navigation process).

Hence, it would be of benefit to have a method and corresponding systemfor confirming correct alignment of the tip of an endoscope afterremoval of a locatable guide used to achieve initial alignment,particularly for procedures involving a target which is obscured fromview.

SUMMARY OF THE INVENTION

The present invention is a system and method for image-based alignmentof an endoscope.

According to the teachings of the present invention there is provided, amethod for confirming correct alignment of a distal end of an endoscopeincluding an imaging arrangement during an endoscopic procedure, themethod comprising: (a) positioning the distal end of the endoscopeadjacent to a target location and capturing a reference image using theimaging arrangement; (b) sensing a real-time video image using theimaging arrangement; and (c) comparing features of the real-time videoimage with the reference image to confirm correct alignment of theendoscope.

According to a further feature of the present invention, the step ofpositioning employs a target location identified in three-dimensionalimage data of a region of a body to be treated.

According to a further feature of the present invention, thethree-dimensional image data is derived from an imaging techniqueselected from: computerized tomography; magnetic resonance imaging;positron emission tomography; and ultrasound.

According to a further feature of the present invention, the step ofpositioning employs a position sensor associated with the distal end ofthe endoscope, the position sensor being part of a position measuringsystem.

According to a further feature of the present invention, the step ofpositioning is performed by comparing the position of the distal end ofthe endoscope as measured by the position measuring system and thetarget location as identified in the image data.

According to a further feature of the present invention, the positionsensor is part of an elongated element deployed within a working channelof the endoscope, and wherein the elongated element is withdrawn fromthe working channel prior to the comparing.

According to a further feature of the present invention, the targetlocation is not visible in the reference image.

According to a further feature of the present invention, the referenceimage and the real-time video image are displayed simultaneously tofacilitate performance of the comparing features visually by a user.

According to a further feature of the present invention, the comparingincludes co-processing the reference image and at least one frame fromthe real-time video to determine a measure of mismatch, the methodfurther comprising generating an alarm signal if the measure of mismatchexceeds a predefined value.

According to a further feature of the present invention, the comparingincludes co-processing the reference image and at least one frame fromthe real-time video to determine a displacement correction required tocompensate for erroneous movement of the endoscope, the method furthercomprising generating a display indicative to a user of the displacementcorrection required to compensate for the erroneous movement of theendoscope.

According to a further feature of the present invention, the comparingincludes co-processing the reference image and at least one frame fromthe real-time video to determine a transformation relating the real-timevideo frame to the reference image, the method further comprisinggenerating a display corresponding to the real-time video with additionof an indication of a target location, position of the indication beingderived at least in part by use of the transformation.

According to a further feature of the present invention, the endoscopeis a bronchoscope.

There is also provided according to the teachings of the presentinvention, a system for ensuring correct alignment of an endoscopeduring performance of an endoscopic procedure, the system comprising:(a) an endoscope having a distal end for insertion into a body; (b) animaging arrangement associated with the endoscope and configured togenerate a real-time video image of a region beyond the distal end; and(c) a processing system associated with the imaging arrangement andconfigured to: (i) in an initial state of alignment with a targetlocation, derive from the imaging arrangement a reference imagecorresponding to correct alignment with the target location, (ii) derivefrom the imaging arrangement real-time images of the region beyond thedistal end, and (iii) co-process the reference image and the real-timeimages to determine a current alignment status of the endoscope with thetarget location.

According to a further feature of the present invention, the processingsystem is configured to co-process the reference image and the real-timeimages to determine a measure of mismatch, the processing system furthergenerating an alarm signal if the measure of mismatch exceeds apredefined value.

According to a further feature of the present invention, there is alsoprovided a display for displaying at least the real-tire images to auser, wherein the processing system is configured to co-process thereference image and the real-time images to determine a displacementcorrection required to compensate for erroneous movement of theendoscope, the processing system further generating an indication on thedisplay indicative to a user of the displacement correction required tocompensate for the erroneous movement of the endoscope.

According to a further feature of the present invention, there is alsoprovided a display for displaying at least the real-time images to auser, wherein the processing system is configured to co-process thereference image and the real-time images to determine a transformationrelating the real-time video frame to the reference image, theprocessing system further generating on the display an indication of atarget location, position of the indication being derived at least inpart by use of the transformation.

According to a further feature of the present invention, there is alsoprovided a position measuring system including a position sensor carriedby an elongated element removably deployable along a working channel ofthe endoscope.

There is also provided according to the teachings of the presentinvention, a method for facilitating performance of an endoscopicprocedure on a target which is obscured from view by an imagingarrangement of an endoscope, the method comprising: (a) generatingreal-time video from the imaging arrangement of the endoscope; (b)determining a position of the target and a position of a distal end ofthe endoscope; (c) generating a display including the real-time videoand a simulated view of the target correctly positioned within thereal-time video; and (d) adjusting the display so as to maintain thetarget correctly positioned within the real-time video when theendoscope is moved.

According to a further feature of the present invention, the adjustingincludes comparing features from at least one frame of the real-timevideo with features from a reference image derived from the imagingarrangement during the step of determining, thereby deriving atransformation relating the real-time video frame to the referenceimage.

According to a further feature of the present invention, the determininga position of a distal end of the endoscope is performed using positionmeasuring system including a position sensor carried by an elongatedelement removably deployable along a working channel of the endoscope.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying, drawings, wherein:

FIG. 1 is a video display of the target zone inside the bronchial treewhen the tip of the bronchoscope is off target.

FIG. 2 is a simulated tip view corresponding to the position of FIG. 1.

FIG. 3 is a video display of the target zone inside the bronchial treewhen the tip of the bronchoscope is on the target.

FIG. 4 is a simulated tip view corresponding to the position of FIG. 3.

FIG. 5 is a display of a combination of a stored image and live video inthe context of first preferred embodiment of the invention.

FIG. 6 is the display of a combination of a stored image and live videoin the context of a second preferred embodiment of the invention.

FIG. 7 is a schematic side cross-sectional view showing the bronchoscopehaving been correctly aligned by use of a position measurement sensorwith a target which is obscured from view.

FIG. 8 is a view similar to FIG. 7 after removal of the positionmeasurement sensor to free a working lumen of the bronchoscope.

FIG. 9 a is a view similar to FIG. 8 after insertion of a tool along theworking lumen.

FIG. 9 b is a view similar to FIG. 9 a after erroneous movement hasdisrupted alignment of the tool with the obscured target.

FIG. 10 is a schematic illustration of the components of a system,constructed and operative according to the teachings of the presentinvention, for ensuring correct alignment of an endoscope duringperformance of an endoscopic procedure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a system and method for image-based alignmentof an endoscope.

The principles and operation of systems and methods according to thepresent invention may be better understood with reference to thedrawings and the accompanying description.

First in general terms, the present invention provides systems andmethods for endoscopic procedures (exemplified herein with reference tobronchoscopic procedures) wherein a first technique is used to ensureinitial correct alignment of an endoscope with a desired target and areference image is acquired from an imaging arrangement associated withthe endoscope. Then, during a subsequent stage of the procedure,tracking of the endoscope position relative to the target is performedpartially or entirely by image-based tracking by comparing features inthe realtime video image produced by the imaging arrangement withfeatures in the reference image.

Thus, according to a first aspect of the present invention, a method forconfirming correct alignment of a distal end of an endoscope during anendoscopic procedure includes: positioning the distal end of theendoscope adjacent to a target location and capturing, a reference imageusing the imaging arrangement; sensing a real-time video image using theimaging arrangement; and comparing features of the real-time video imagewith the reference image to confirm correct alignment of the endoscope.

It will immediately be appreciated that the present invention offersprofound advantages, particularly for cases where the desired target isobscured from view (such as behind other tissue) or is not readilyidentifiable directly by visual imaging. In such cases, navigation undervideo imaging alone is insufficient. Nevertheless, after use of aprimary tracking system (such as that of the aforementioned WO03/086498) to achieve initial alignment, use of feature-based opticaltracking based on features not necessarily belonging to the target freesthe system from subsequent dependence on the primary tracking system,thereby allowing removal of the position measurement probe and/orrendering navigation more robust and reliable in the face ofdisturbances such as movement of the patient's body or the like. Theseand other advantages of the present invention will become clearer fromthe subsequent description.

Referring now to the drawings, FIG. 10 shows schematically a preferredimplementation of a system, constructed and operative according to theteachings of the present invention, for implementing the methods of thepresent invention. For one set of preferred implementations of themethod of the present invention, the system is substantially similar tothat described in WO 03/086498 with certain changes to the displayand/or image processing systems, as will be described below. Thus, aposition measurement sensor 101 and video sensor 102 are incorporated inthe distal tip of bronchoscope 100. An electro-magnetic tracking systeminduces electro-magnetic fields from antennae 107, senses the signalsfrom the location sensor 101 and determines the position of the tip ofthe bronchoscope in six degrees of freedom. A processing system 108gathers that position information together with the video image from thetip of the bronchoscope as produced by the video camera 104. Theprocessing system may display to the physician live video, capturedimages and simulated views on a display screen 110.

Further details of a particularly preferred position measuring systemfor measuring position in six degrees-of-freedom may be found in U.S.Pat. No. 6,188,355 and PCT Application Publication Nos. WO 00/10456 andWO 01/67035 Most preferably, at least one, and preferably three,reference sensors (not shown) are also attached to the chest of thepatient and their 6 DOF coordinates sent to processing system 108 wherethey are used to calculate the patient coordinate frame of reference.

It should be noted in this context that the term “position sensor” isused herein in the description and claims to refer to any element whichcan be associated permanently or temporarily with an object andfunctions together with other components of a position measuring systemto determine the position and/or attitude of the object. It should beappreciated that the terminology does not necessarily imply that theposition sensor itself is capable of any measurement alone. Nor doesthis terminology imply any particular function of the position sensor,such that the “sensor” may be a transmitter, a receiver or any otherelement which functions as part of a position measuring system,depending upon the technology employed. In all such cases, the elementis referred to as a “position sensor” since its presence associated withthe object allows sensing by the system of the object's position.

Although described herein with reference to a non-limiting preferredimplementation employing a bronchoscope, it should be noted that thepresent invention is equally applicable to substantially any intra-bodyendoscopic procedure.

As in the aforementioned WO 03/086498, the location of the desiredtarget within the body is preferably determined in an offlinepreparation session prior to the procedure in which the target isidentified in three-dimensional image data of a region of a body to betreated. The three-dimensional image data is preferably derived from animaging technique selected from: computerized tomography; magneticresonance imaging; positron emission tomography; and ultrasound. Mostcommonly, computerized tomography (“CT”) data is used. Then, aftersuitable calibration to register the position measurement systemcoordinates with the CT data, a simulated tip view or other visualnavigation aids as described in WO 03/086498 are used to guide thebronchoscope into alignment with the target. These navigation aids arebased on comparing the position of the distal end of the endoscope asmeasured by the position measuring system and the target location asidentified in the image data. Then, according to one particularlypreferred set of embodiments, the position sensor is withdrawn from aworking channel of the endoscope as part of an elongated element.

FIGS. 1-4 illustrate schematically examples the displays which arepreferably available to the physician during initial alignment of thebronchoscope. Specifically, FIG. 1 shows an example of a target area.The target is obscured from view, being located behind the tissue of abifurcation inside the bronchus. The target 10, marked in a broken line,is not visible in the video image. In one embodiment of the invention,it is not marked in the video display at all. In another preferredembodiment it's the target's location, as calculated by the processingsystem 108, is displayed in the video display by an artificial mark suchas a line, a point, a broken line, a colored area, a three dimensionalentity or a combination of any of the above.

In FIG. 1, the tip of the bronchoscope is shown to be positioned off thedirection of the target. FIG. 2 is the tip view used for directing tothe target. The direction of the target relative to the tip is presentedby dot 20 marking the target and arrow 22 aiming from the tip to thetarget. The target may also be presented in a simulated view of theboundary of the actual target lesion as calculated from the CT data orby a colored area or by three-dimensional entity or by any combinationof the above. According to the example, the tip should be deflecting inthe 12 o'clock direction in order to be on target FIGS. 3 and 4 show thesame scenario when the tip is on target. According to the prior artdescribed above, after achieving alignment with the target as shown, thephysician has to try to hold the bronchoscope steady while withdrawingthe locatable guide and inserting a tool along the lumen. According tothe present invention, before the guide is withdrawn, the image as shownin FIG. 3 is captured and stored in a memory device of processing system108. Now the system has two sources of images to control the location ofthe bronchoscope's distal tip, a real-time live video image 52 and acaptured video image 51 where the tip was located at the desired targetlocation, as shown in FIG. 5.

The present invention may be implemented in a number of differentembodiments with different degrees of sophistication as to how thecomparison between features of the real-time video and the referenceimage is performed. According, to a first basic embodiment, thereference image 51 and the real-time video image 52 are displayedsimultaneously on display device 110 as illustrated in FIG. 5, therebyfacilitating visual comparison of the image features by a user. In thiscase, the physician himself compares the two images and decides whetherthe bronchoscope is located in the required location, and if not, inwhat direction the tip of the bronchoscope should be deflected.

In more sophisticated embodiments, the system preferably co-processesthe reference image and the real-time images to determine a currentalignment status of the endoscope with the target location. Thus,processing system 108 is configured to: derive from the imagingarrangement of the endoscope, in an initial state of alignment with atarget location, a reference image corresponding to correct alignmentwith the target location; derive from the imaging, arrangement real-timeimages of the region beyond the distal end, and co-process the referenceimage and the real-time images to determine a current alignment statusof the endoscope with the target location.

Here too, the co-processing may be implemented at various differentlevels of sophistication. In a simplest case, a correlation between thereference image and the current video image may offer a measure ofmismatch. The user can then empirically adjust the position of thebronchoscope tip to maximize the correlation (minimize the mismatch),thereby returning to the correct position. Application of a threshold tothe measure of mismatch may be used to activate an alarm signal.

In more preferred implementations, the system tracks features or regionsfrom the reference image in the video image to provide more specificindications to the user of the required correction for any erroneousmovement of the bronchoscope off target. For small-scale lateraldisplacements, this may be implemented simply by correlating a centralsub-window 56 of reference image 51 centered on target location 55 witha corresponding sized sliding window (i.e., at multiple differentpositions) in the real-time video to find the best match, therebyidentifying the position of the target sub-window in the real-time videoimage.

At a next level of sophistication the tracking may also allow forscaling and/or rotation of the sub-window. This allows the system tomaintain target tracking during rotation, as well as small-scaleadvancing or withdrawal, of the bronchoscope. A further level ofsophistication may employ planar transformations such as affinetransformations which approximate the distortions caused by viewing asurface from different viewing angles.

At the top end of the range of sophistication in the tracking algorithmsare tracking techniques based on three-dimensional modeling of theviewed scene and reconstruction of the camera path. Such techniques,often referred to as “Structure from Motion”, are well developed in thefield of optical tracking and computer vision, and allow reconstructionof three-dimensional models from a single moving camera. Details ofprocessing techniques for implementing structure from motion may befound in papers from the Robotics Research Group in the Department ofEngineering Science, Oxford University (UK) such as “Automatic CameraTracking” by Andrew W. Fitzgibbon et al. Video Registration (2003) and“Feature Based Methods for Structure and Motion Estimation” by P. H. S.Torr et al. Vision Algorithms: Theory and Practice (2000), bothavailable from http://www.robots.ox.ac.uk/.

In the present application, structure-from-motion processing can begreatly simplified by the use of model data based on CT data or thelike. Thus, for example, given that the initial reference image is takenfrom a known position as established by the primary alignment system, a“depth” (i.e., camera-to-surface distance) associated with each pixel ofthe reference image can be derived directly from CT data, therebyproviding an initial three-dimensional model from which processing canbegin. This approach has advantages of robustness under significantchanges of view, and even where there is no overlap between the currentreal-time video field of view and the reference image.

In any or all of the above-mentioned tracking techniques, correctionsare preferably made for geometrical distortions introduced by the opticsof the imaging arrangement, as is known in the art. These correctionsmay be performed on the source images prior to implementing the trackingtechniques, or may be incorporated into the tracking calculationsthemselves.

The output from the system (and method) of the present invention maytake a number of forms. In a simplest case mentioned above, an alarm maybe sounded if a measure of mismatch between the current video and thereference image indicates that the bronchoscope has wandered off target,and the measure of mismatch (or the correlation) may be displayed to theuser or indicated by an audio signal to provide feedback indicative of“getting hotter” or “getting colder” with regard to alignment with thetarget.

In more preferred implementations where features of the reference imageare positively tracked within the real-time video, the processing systemmay generate an indication on the display indicative to a user of thedisplacement correction required to compensate for the erroneousmovement of the endoscope. This may take the form of all arrow or vectorsuch as line 62 in FIG. 6 which indicates the movement of thebronchoscope required to bring the center of the field of view intoalignment with the target position illustrated as 61. Thus, FIG. 6corresponds to the display when the bronchoscope is in the position ofFIG. 9 b. After performing the required corrective motion, thebronchoscope returns to the position of FIG. 9 a and the live video 52of FIG. 6 would again appear similar to the reference image 51.

Alternatively, or additionally, a transformation (2 or 3 dimensional)calculated by the processing system for relating the real-time videoframe to the reference image may be used to determine the position ofthe obscured target within the real-time video image. The targetlocation can then be designated in the real-time video image, forexample, by the sub-window frame 58 or the marker 57 as shown in FIG. 5.

According to a most preferred option, which is believed to be ofpatentable significance in its own right, the present invention providesan augmented reality endoscopic display in which a simulated view of anobscured target is displayed in the context of the real-time video sothat the target appears correctly positioned within the video image andmoves so as to maintain the correct positioning of the target within thereal-time video when the endoscope is moved. This augmented realitydisplay allows the user to operate the endoscope in a fully intuitivemanner as if the target were directly viewable via the video imagingarrangement of the endoscope. Thus, the user will see obscured target 10of FIGS. 1 and 3 as if the tissue in front of the target wassemi-transparent.

In practical terms, the simulated view of the target used for theaugmented reality display is preferably derived from three-dimensionalimaging data such as CT in which the target tissue has been designatedprior to the procedure. The target tissue volume is then preferablyexported as a three-dimensional graphic object, or a closed bodygeometrical approximation to the tissue volume is generated. Then,during the procedure, information regarding the relative positions andorientations of the endoscope tip and the target tissue is used todetermine the position, viewing angle and scaling factors which shouldbe used to represent the target correctly in the real-time video image.The target is preferably indicated as a semi-transparent video overlayso that it appears as a ghost image without completely hiding the tissueactually viewed in the video image. Alternatively, a dashed outline orany other suitable indication may be used.

The augmented reality display is advantageous both during initialalignment of the endoscope with the target and during subsequentperformance of a procedure. Most preferably, during a procedure,real-time adjustment of the simulated target image within the videoimage is performed on the basis of the optical tracking of the presentinvention. Where optical tracking is performed in two dimensions only,the adjustment of the target appearance will correspondingly be reducedto a two-dimensional manipulation. Where three-dimensional model basedtracking is used, full three-dimensional augmented reality functionalityis preferably maintained.

In each case, an alarm is preferably activated if the location error,i.e., the misalignment of the real-time video from the reference image,exceeds a predefined value, for example, the size of the target. Thealarm may be an audio alarm and/or a visual alarm indication such as aflashing symbol or a color change of part or all of the display. Analarm (which may be distinct from the off-target alarm) is preferablyalso generated if the tracking algorithm fails to maintain reliabletracking between the reference image and the current image.

As mentioned earlier, the optical tracking of the present invention doesnot require the target location to be visible in the reference image. Infact, it should be noted that the reference image need not even includethe direction to the target in its field of view. For example, if anendoscope is to be used in a procedure with a tool which generatesimages, takes samples or otherwise treats a region of tissue locatedlaterally next to the distal end of the endoscope, the imagingarrangement of the endoscope will typically not offer a view of thetissue of the target, nor of any tissue which overlies the target.Nevertheless, once correct alignment of the endoscope has been achievedusing the primary tracking system, the optical tracking of the presentinvention based on a reference image of the scene beyond the tip of theendoscope is effective to ensure correct alignment with the target,despite the fact that the target is outside the field of view.

It will be appreciated that the above descriptions are intended only toserve as examples, and that many other embodiments are possible withinthe scope of the present invention as defined in the appended claims.

What is claimed is:
 1. A method for confirming correct alignment of adistal end of an endoscope including an imaging arrangement during anendoscopic procedure, the method comprising: positioning the distal endof the endoscope adjacent to a target location and capturing a referenceimage using the imaging arrangement; sensing a real-time video imageusing the imaging arrangement; comparing features of the real-time videoimage with the reference image to determine whether the endoscope iscorrectly aligned; if the endoscope is not correctly aligned: measuringa mismatch between the reference image and the real-time video image;providing a visual indication of the mismatch, the visual indicationincluding directionality and magnitude information; and adjusting aposition of the endoscope based on the directionality and magnitudeinformation derived from the mismatch; and correlating a sub-window ofthe reference image provided on a display, and centered on the targetlocation, with a corresponding sliding window of the real-time videoimage provided on the display.
 2. The method of claim 1, wherein saidstep of positioning employs a target location identified inthree-dimensional image data of a region of a body to be treated.
 3. Themethod of claim 2, wherein said three-dimensional image data is derivedfrom an imaging technique selected from: computerized tomography;magnetic resonance imaging; positron emission tomography; andultrasound.
 4. The method of claim 1, wherein the positioning stepemploys a position sensor associated with the distal end of theendoscope, said position sensor configured to aid in the measuring ofthe mismatch between the reference image and the real-time video image.5. The method of claim 4, wherein the positioning step is performed bycomparing a position of the distal end of the endoscope as measured inthe measuring step and the target location.
 6. The method of claim 4,wherein said position sensor is part of an elongated element deployedwithin a working channel of the endoscope, and wherein said elongatedelement is withdrawn from the working channel prior to said comparingstep.
 7. The method of claim 1, wherein said target location is notvisible in said reference image.
 8. The method of claim 1, furthercomprising displaying simultaneously said reference image and saidreal-time video image to facilitate the visual indication of themismatch.
 9. The method of claim 1, wherein said comparing step includesco-processing said reference image and at least one frame from thereal-time video image, the method further comprising generating an alarmsignal if the visual indication of the mismatch exceeds a predefinedvalue.
 10. The method of claim 1, wherein said comparing includesco-processing said reference image and at least one frame from saidreal-time video to determine a displacement correction required tocompensate for erroneous movement of the endoscope, the method furthercomprising generating a display indicative to a user of saiddisplacement correction required to compensate for the erroneousmovement of the endoscope.
 11. The method of claim 1, wherein saidcomparing includes co-processing said reference image and at least oneframe from said real-time video to determine a transformation relatingsaid real-time video frame to said reference image, the method furthercomprising generating a display corresponding to said real-time videowith addition of an indication of a target location, position of saidindication being derived at least in part by use of said transformation.12. The method of claim 1, wherein the endoscope is a bronchoscope. 13.A system for ensuring correct alignment of an endoscope duringperformance of an endoscopic procedure, the system comprising: anendoscope having a distal end for insertion into a body; an imagingarrangement associated with said endoscope and configured to generate areal-time video image of a region beyond said distal end; and aprocessing system associated with said imaging arrangement andconfigured to: (i) in an initial state of alignment with a targetlocation, derive from said imaging arrangement a reference imagecorresponding to correct alignment with the target location, (ii) derivefrom said imaging arrangement real-time images of the region beyond saiddistal end, (iii) co-process said reference image and said real-timeimages to determine a current alignment status of said endoscope withthe target location, (iv) if said endoscope is not currently aligned:measure a mismatch between the reference image and the real-time videoimage; provide a visual indication of the mismatch, the visualindication including directionality and magnitude information; andadjust a position of the endoscope based on the directionality andmagnitude information derived from the mismatch; and (v) correlate asub-window of the reference image provided on a display, and centered onthe target location, with a corresponding sliding window of thereal-time video image provided on the display.
 14. The system of claim13, wherein said processing system is configured to co-process saidreference image and said real-time images, said processing systemfurther generating an alarm signal if the visual indication of themismatch exceeds a predefined value.
 15. The system of claim 13, furthercomprising a display for displaying at least said real-time images to auser, wherein said processing system is configured to co-process saidreference image and said real-time images to determine a displacementcorrection required to compensate for erroneous movement of theendoscope, said processing system further generating an indication onsaid display indicative to a user of said displacement correctionrequired to compensate for the erroneous movement of the endoscope. 16.The system of claim 13, further comprising a display for displaying atleast said real-time images to a user, wherein said processing system isconfigured to co-process said reference image and said real-time imagesto determine a transformation relating said real-time video frame tosaid reference image, said processing system further generating on saiddisplay an indication of a target location, position of said indicationbeing derived at least in part by use of said transformation.
 17. Thesystem of claim 13, further comprising a position sensor carried by anelongated element removably deployable along a working channel of saidendoscope.